1. Field of the Invention
The present invention relates to a surface-mount type electronic component package in which an electronic component such as an IC is mounted, a circuit board, an electronic component mounted apparatus, and a method of inspecting a bonding portion therein.
2. Description of Related Art
Recently, as electronic equipment becomes smaller in size and more advanced in functionality, area array type IC packaging in which solder lands are provided on the bottom, such as BGA (Ball Grid Array) type and LGA (Land Grid Array) type CSP (Chip Size Packaging), is used widely to mount electronic components.
FIG. 17 is an enlarged cross-sectional conceptual diagram of a bonding portion of a conventional electronic component mounted apparatus in which a BGA package is mounted on a circuit board by soldering. The electronic component mounted apparatus 101 includes a BGA package (hereinafter referred to as an “electronic component package”) 103 mounted on a circuit board 102. The circuit board 102 includes circuit board-side lands 106 that are disposed on an insulating substrate 105, and a part of which is covered with a circuit board-side resist 110.
The electronic component package 103 includes a carrier substrate 107, an IC chip (not shown) that is disposed on the upper surface 107a of the carrier substrate 107, external connection lands 108 that are disposed on the lower surface 107b of the carrier substrate, and a part of which is covered with a resist 111, and solder balls 104 that are disposed on the external connection land 108. The solder balls 104 connect the circuit board-side lands 106 and the external connection lands 108.
A method of manufacturing an electronic component mounted apparatus 101 with this configuration will be described next. First, an IC chip is mounted on the upper surface 107a of an insulating carrier substrate. Next, solder balls 104 are bonded to external connection lands 108 to form an electronic component package 103. A cream solder (not shown) is then applied onto circuit board-side lands 106. The external connection lands 108 and the circuit board-side lands 106 are positioned such that they face each other, and the solder balls are bonded to form bonding portions 109. An electronic component mounted apparatus 101 is manufactured through the above-described steps.
FIG. 18 shows cross sections i1 to i5 that are obtained by slicing a bonding portion 109 of FIG. 17 at slicing planes I1 to I5. Cross section i1 is the shape of the external connection land 107 that is free from the resist 111. Cross section i5 is the shape of the circuit board-side land 106 that is free from the resist 110.
Ordinarily, the cross sections i1 and i5 have a circular shape. Cross section i2 is slightly larger than cross section i1, and cross section i3 is the maximum cross-sectional region of the molten solder ball, which is the largest in size. Similarly, cross section i4 is slightly larger than cross section i5.
However, if the solder ball 104 and the external connection land 108 do not wet, the cross sectional shape increases discontinuously, irregularly, or the cross section i2 may be too small, rather than increasing almost continuously from cross sections i1 to i2. This phenomenon is difficult to detect by external visual inspection.
This defective solder wetting is caused by warping of the substrate due to heat generated during reflowing, weak activity of flux, random variations in solder ball size, or the like. If the solder ball has poor wettability, the bonding between the circuit board-side land and the external connection land will be defective.
As shown in FIG. 17, X-rays (direction of arrow) are irradiated from the upper side to the lower side in the diagram, and received by an X-ray-receiving apparatus (not shown) located in the lower side to create X-ray image data, and an X-ray image is displayed. The density is almost uniform within the shape of the smaller of the slicing planes I1 and I5, but the number of X-rays increases gradually toward the outer side. When this is expressed in X-ray image density, the density becomes gradually lighter from the inside toward the outside. However, in this configuration, the cross sections i1 and i2 cannot be distinguished, and it is therefore difficult to determine the acceptability of the wettability.
Further, because the transmission cross sections of the land and the solder ball have a similar circular shape, the boundary or contour of each shape does not appear clearly in X-ray image density, and it is therefore further difficult to distinguish the cross sections i1 and i2.
Also, because the solder ball is spherical and the land is circular, an X-ray image is displayed in the shape of a circle regardless of whether or not the solder ball wets and spreads, and it is therefore difficult to determine the acceptability of wettability (bondability with the land).
As a method of solving the above problem, an electronic component mounted apparatus has been disclosed in which circuit board-side lands are provided with a polygonal shape such as a quadrilateral shape (see, for example, JP H10-335796A).
With this configuration, if a solder ball has satisfactory wettability, the shape of the circuit board-side solder ball conforms to that of the land, and thus the X-ray image of the solder ball will not be circular. Based on this, it is possible to determine the acceptability of bondability of the bonding portion. Because the bondability can be determined nondestructively, the reliability of circuit boards and electronic circuit apparatuses can be increased.
Another technique has been disclosed in which a ceramic substrate is used as a chip carrier, and external connection lands are formed on the underside of the chip carrier, which are square in shape (see, for example, JP H8-274213A). This increases the connection area of a land with the carrier substrate. It is therefore possible to form an electronic component package in which the lands have a strong bonding strength.
Ordinarily, a molten solder ball to be bonded tends to form a circular shape due to surface tension, so that in a land configured as above, the straight portions are unlikely to be wetted with solder. Further, because the land has no arc portion (a portion of the perimeter of the land that has an arc shape), if one of the straight portions (portions of the perimeter of the land that are linear) of the land shape is not wetted with solder, the periphery of the other straight portions are unlikely to be wetted with solder, and the shape of the molten solder ball will be deformed considerably. This results in the problem that the occurrence of bonding failures between the circuit board-side land and the solder ball increases, and connection reliability is degraded.